Shipping and aviation represented around 3.2 and 2.1 per cent respectively of global CO2 emissions in the mid-2000s. A wide range of projections and scenarios shows that both sectors are likely to grow over the coming decades with a resultant increase in CO2 emissions by 2050, despite mitigation efforts through technology, operations, and usage of low-carbon fuels.
If current projections of emissions from shipping and aviation to 2050 are placed in the context of an overall global 2°C emissions reduction pathway, then shipping might contribute between approximately 6 and 18 per cent of median permissible total CO2-equivalent emissions in 2050 to meet the pathway, and aviation might contribute between approximately 4 and 15 per cent, according to a recent study published by Transport & Environment.
Report: Shipping and aviation emissions in the context of a 2°C emission pathway (March 2013). By D. S. Lee, Ling Lim, and B. Owen, Manchester Metropolitan University.